The invention relates to a multi-voltage on-board power supply system for a motor vehicle having a hybrid or electric drive, comprising a dc-dc converter, by means of which a high voltage level having a higher direct-current voltage different from ground and at least a first energy storage device is connected to a low voltage level having a lower voltage different from ground and at least a second energy storage device.
Such multi-voltage on-board power supply systems having dc-dc converters are known, in many cases, from the state of the art. A dc-dc converter can connect on-board energy supply systems of different voltages with respect to energy. For increasing the power density of the dc-dc converter and for increasing its current load capacity, dc-dc converters often have a multiphase configuration. Preferably, this is a parallel connection of several converter phases (which is assumed in the following). In the case of a staggered controlling of the power switches (by 360 degrees divided by the number of converter phases), the current ripples are superimposed on one another at the output terminals and bus capacitors, whereby component stress can be reduced particularly at the bus capacitors.
In the state of the art, multi-voltage on-board power supply systems are used, among other things, for increasing the peak capacity (for example, hybrid drive, electrification of accessories). These partial power supply systems are connected by efficient multi-voltage converters which typically have a multiphase configuration.
It is an object of the invention to cost-effectively expand the functionality of a multi-voltage on-board power supply system.
This object is achieved by a multi-voltage on-board power supply system according to claim 1. Advantageous embodiments and further developments of the invention are contained in the dependent claims.
In contrast to the providing of a separate charging set—in addition to the dc-dc converter—the invention leads to a reduction of expensive, heavy and voluminous components. The total costs can thereby be reduced and the required space can be minimized. In addition, weight and therefore fuel can be saved.
The functional and constructional integration of charge sets into a motor vehicle per se is known from the state of the art. As a result of the integration of a suitable charge set, external equipment, such as small electrorollers, can be charged in a practical manner in future motor vehicles, particularly city vehicles. The possibility of charging an external device in a motor vehicle on-board energy supply system represents a function that is extremely valuable to customers. The charge sets known from the state of the art frequently contain their own dc-dc converters by means of which the respective external device can be charged by the on-board energy supply system of the motor vehicle.
According to the invention, at least one converter phase of the dc-dc converter provided anyhow for the various voltage levels of the multi-voltage on-board power supply system is used for charging the external device.
For this purpose, a charging interface for charging external devices is provided in the case of the multi-voltage system. The multi-voltage system and particularly the dc-dc converter or its wiring are implemented such that at least one converter phase of the dc-dc converter can be disconnected from the low voltage level and instead can be connected with the charging interface. In addition, a third energy storage device—to be charged—is provided which preferably is a component of the external device and which can be connected to the charging interface. In the state connected to the charging interface, this third energy storage device is supplied with the lower voltage of the multi-voltage supply system, and a charging of the third energy storage device by the energy flow from the first energy storage device to the third energy storage device is thereby permitted.
The multi-voltage on-board power supply may be implemented particularly as a two-voltage on-board power supply system with exclusively one high voltage level and one low voltage level.
In the simplest case, the dc-dc converter is implemented in a single-phase fashion. The single converter phase of the dc-dc converter can then be disconnected from the low voltage level and can instead be connected with the charging interface.
According to a preferred embodiment of the present invention, however, the dc-dc converter comprises several parallel-connected converter phases. It can then preferably be operated in at least a first and a second operating mode. In the first operating mode, all converter phases of the dc-dc converter are connected with the second energy storage device, and no converter phase is connected with the charging interface. The dc-dc converter will then be available exclusively for the voltage conversion between the high voltage level and the low voltage level. In contrast, in the second operating mode, at least one converter phase of the dc-dc converter is connected with the second energy storage device, and at least one other converter phase of the dc-dc converter is connected with the charging interface. The converter phases of the dc-dc converter are therefore partly utilized for charging the third energy storage device but also partly continue to be available for the voltage conversion between the high voltage level and the low voltage level.
In order to reduce component stress, particularly for a bus capacitor optionally connected on the part of the high voltage level parallel to the first energy storage device, the converter phases can be controlled in a staggered manner in the second operating mode.
The lower voltage (low voltage level) preferably is an on-board power supply system of approximately 12 volt that is typical of motor vehicles. The high voltage level is preferably connected with a traction battery of the motor vehicle or of the hybrid or electric drive of the motor vehicle.
The above-mentioned disconnecting of a converter phase from the low voltage level and its connecting with the charging interface can preferably be carried out by a single electronically controllable switching element. The operating modes can thereby be changed particularly easily, and the change-over can take place in a synchronized manner.
If the dc-dc converter comprises more than two converter phases, by means of suitable switch-over devices, a variable division of the total performance of the dc-dc converter between the “tasks” of the dc-dc conversion and the charging of exterior devices can be made possible. Thus, for example, when N converter phases are present, optionally one converter phase or two converter phases or up to (N−1) converter phases can be geared toward the charging of external devices, while the remaining converter phases will continue to be available for the dc-dc conversion.
The switch-over devices (possibly implemented as a single electronically controllable switching device) for disconnecting at least one converter phase from the low voltage level and for connecting it with the charging interface, are preferably integrated together with the converter phases of the dc-dc converter into an equipment component or into a housing. In addition, possibly provided bus capacitors are preferably also integrated into this equipment component or into this housing.
The charging interface is preferably constructed as a plug contact or as a switch. An external device can particularly easily be connected to a plug contact. In particular, a possible plug contact preferably has a standardized charging socket compatible with an external device that is standardized with respect to its charging plug.
According to a preferred embodiment of the present invention, a connecting of a third energy storage device to the charging interface can be detected and, as a function of this detection, the disconnecting from the low voltage level and the connecting with the charging interface can be automatically controlled. In particular, preferably the above-mentioned switch-over devices (especially if they are constructed as a single electronically controllable switching element) can be controlled as a function of this detection. The change of the operating modes can then take place automatically as soon as an external device to be charged is connected to the charging interface.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.